The memory or bit cell is the fundamental building block of memory. It can be implemented using different technologies, such as bipolar, metal-oxide semiconductor (MOS), and other semiconductor devices. It can also be built from magnetic material such as ferrite cores or magnetic bubbles. Regardless of the implementation technology used, a memory or bit cell generally stores one bit of binary information.
Typically bit cells are arranged into words (e.g., an 8-bit word, 32-bit word, and 128-bit word), and are accessed (read from or written to) in a group. Often a word line will transmit a signal that provides access to or activates the entire word. The information read from or written to the bit cell is transmitted via a bit line that accesses a specific bit of the word. Memory or bit cells are typically arranged in arrays. In these arrays the words are often thoughts of as the rows, and the bits or bit lines are thought of as the columns.
Occasionally a bit cell is susceptible to a type of error known as a read disturb. The susceptibility of bit cells to read disturb errors generally gets worse as transistor parametric variation increases with more aggressive technology scaling. It is well understood that smaller feature sizes have less well-controlled electrical characteristics, and there is a higher statistical probability of non-ideal behavior. A read disturb error occurs when the bit cell is being read from, but the voltages and currents are such that instead of reading from the bit cell in a non-destructive manner, the value stored in the bit cell changes. The voltage applied by the word line is sufficiently high that a high bit value is written into the bit cell, overwriting a properly stored low bit value. Errors such as this are undesirable. Often the likelihood of such an error increases as the rows, words or word size per bit line (or column) increase. This can limit the size of the memory array.